1. Field of the Invention
The present invention relates to a fusing roller used with an image forming apparatus and a method of manufacturing the same.
2. Description of the Related Art
As generally known in the art, an electrophotographic image forming apparatus comprises a laser scanning unit, a photosensitive member, a developing device and a fusing roller. The laser scanning unit generates laser light and emits it to the photosensitive member so that an electrostatic latent image can be formed on the surface of the photosensitive member. The developing device affixes a toner to the electrostatic latent image formed on the surface of the photosensitive member in order to develop the electrostatic latent image, thereby producing a visible developed toner image. The toner image is transferred onto a printing paper passing between the photosensitive member and the fusing roller. The toner image is fused and stuck on the printing paper by heat and pressure when the printing paper passes between the fusing roller and a backup roller which rotates in contact with the fusing roller.
The fusing roller generates a high-temperature heat when supplied with power generally from an external source, and includes a resistor to generate a resistance heat between outer and inner metal pipes having different diameters.
FIG. 1 is a schematic view of a conventional fusing roller for an image forming apparatus. Referring to FIG. 1, an expandable pipe 11 of a conventional fusing roller 10 has an insulating layer on the outer surface thereof. Also, a heating coil 12 to generate heat is wound around the expandable pipe 11. The heating coil 12 is connected to a terminal block 13 to receive an external power. The expandable pipe 11 with the heating coil 12 wound thereon is inserted into a heating pipe (not shown) with an insulating layer on the inner circumference thereof. The external diameter of the expandable pipe 11 is then expanded so that the expandable pipe 11 can come into close contact with the heating pipe.
In the conventional fusing roller 10, the heating coil 12 is connected to the terminal block 13 by a single winding at one end of the terminal block 13. Since the heating coil 12 repeats expansion and contraction by the repeated power supply and suspension, the connection between the heating coil 12 and the terminal block 13 may be weakened. When the expandable pipe 11 is inserted into the heating pipe, its external diameter is expanded. If the outer circumference of the expandable pipe 11 does not closely contact the inner circumference of the heating pipe, the connection between the heating coil 12 and the terminal block 13 will become unstable. The weakened or unstable connection between the heating coil 12 and the terminal block 13 may generate a contact resistance between the heating coil 12 and the terminal block 13. This may cause local overheating and sparks, thereby resulting in disconnection between the heating coil 12 and the terminal block 13. Consequently, the fusing roller 11 can be overheated.